Negatively-charged oxygen atom producing method and producing apparatus

ABSTRACT

The present invention provides a method for producing negatively charged oxygen atoms comprising: placing a negative electrode ( 3 ) on a surface of a member ( 2 ) made of calcium-aluminum composite oxide, proximately placing a positive electrode ( 10 ) on a side of the member opposite to the surface on which the negative electrode is placed, supplying oxygen to the negative electrode side, and applying voltage between the negative electrode and the positive electrode so as to extract negatively charged oxygen atoms (A) from the side where the positive electrode ( 10 ) is placed. The present invention also provides an apparatus for producing negatively charged oxygen atoms which is used for the above method.

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing negativelycharged oxygen atoms and an apparatus for producing negatively chargedoxygen atoms which may be employed for the aforementioned method.Negatively charged oxygen atoms are represented by O⁻ and come in veryuseful in various fields, for example, for oxidative reaction in gaseousphase, fabrication of silicon oxidized film in semiconductormanufacturing process, mildew-proof treatment of fruits such asstrawberries, maintaining sea food freshness such as maintaining tunafreshness.

As a method for producing negatively charged oxygen atoms, it is knownto bring low-energy electrons to adhere to oxygen atoms generated byelectric discharge and the like, thereby producing negatively chargedoxygen atoms. However, this method has a problem that high vacuum isrequired for causing electric discharge and a problem in view of energy.

Another known method is a method in which ozone is generated by electricdischarge in an oxygen gas, the resulting ozone is irradiated withultraviolet rays, whereby low-energy electrons adhere to the resultingoxygen to produce negatively charged oxygen atoms (JP62237733A).However, this method has a problem that a large quantity of dischargeenergy is required for generating ozone.

The present invention aims to provide a method and an apparatus foreffectively producing negatively charged oxygen atoms without requiringsuch high vacuum and such discharge energy.

DISCLOSURE OF THE INVENTION

The present invention provides a method for producing negatively chargedoxygen atoms comprising: placing a negative electrode on a surface of amember made of calcium-aluminum composite oxide; placing a positiveelectrode on a side of the member opposite to the surface on which thenegative electrode is placed; supplying oxygen to the negative electrodeside; and applying voltage between the negative electrode and thepositive electrode so as to extract negatively charged oxygen atoms fromthe side where the positive electrode is placed.

In the method for producing negatively charged oxygen atoms, the voltageis applied while heating the member to a temperature of from 200° C. to1000° C.

In the method for producing negatively charged oxygen atoms, thecalcium-aluminum composite oxide is prepared by baking a mixture ofcalcium carbonate and aluminum oxide.

In the method for producing negatively charged oxygen atoms, thecalcium-aluminum composite oxide is prepared by baking the calciumcarbonate and the aluminum oxide at a baking temperature of from 1300°C. to 1450° C.

In the method for producing negatively charged oxygen atoms, the calciumcarbonate and the aluminum oxide are baked in dry oxygen atmosphere ofwhich oxygen partial pressure is 10 kPa or more and the vapor partialpressure is 10⁻³ Pa or less.

In the method for producing negatively charged oxygen atoms, thecalcium-aluminum composite oxide has a molar ratio between calciumcarbonate and aluminum oxide is 12:7.

The present invention provides an apparatus for producing negativelycharged oxygen atoms having an oxygen supply compartment and anegatively charged oxygen atom producing compartment which are definedby arranging a member made of calcium-aluminum composite oxide, theapparatus comprising a heating means disposed on the member made ofcalcium-aluminum composite oxide, a negative electrode placed on asurface of the member facing the oxygen supply compartment, a positiveelectrode placed in the negatively charged oxygen atom producingcompartment on a side of the member opposite to the surface on which thenegative electrode is placed, and a power source for applying voltagebetween the positive electrode and the negative electrode.

In the apparatus for producing negatively charged oxygen atoms, thepositive electrode is placed on the side of the member made ofcalcium-aluminum composite oxide opposite to the surface of the memberon which the negative electrode is placed such that the positiveelectrode is spaced apart from the member made of calcium-aluminumcomposite oxide.

In the apparatus for producing negatively charged oxygen atoms, in placeof the positive electrode, a conductive target object to be processed isplaced on the side of the member made of calcium-aluminum compositeoxide opposite to the surface of the member on which the negativeelectrode is placed such that the conductive target object is spacedapart from the member made of calcium-aluminum composite oxide, andwherein voltage is applied between the conductive target object and thenegative electrode.

In the apparatus for producing negatively charged oxygen atoms, thepositive electrode is placed on a spacer which is attached to thesurface of the member made of calcium-aluminum composite oxide oppositeto the surface of the member on which the negative electrode is placed.

In the apparatus for producing negatively charged oxygen atoms, acontrol electrode is arranged between the positive electrode and thetarget object to be processed with negatively charged oxygen atoms.

In the apparatus for producing negatively charged oxygen atoms, thecalcium-aluminum composite oxide is prepared by baking a mixture ofcalcium carbonate and aluminum oxide.

In the apparatus for producing negatively charged oxygen atoms, thecalcium-aluminum composite oxide has a molar ratio between calciumcarbonate and aluminum oxide is 12:7.

The present invention also provides a processing equipment forconducting process by negatively charged oxygen atoms having an oxygensupply compartment and a negatively charged oxygen atom producingcompartment which are defined by arranging a member made ofcalcium-aluminum composite oxide, the processing equipment comprising aheating means disposed on the member made of calcium-aluminum compositeoxide, a negative electrode placed on a surface of the member facing theoxygen supply compartment, a positive electrode placed in the negativelycharged oxygen atom producing compartment on a side of the memberopposite to the surface on which the negative electrode is placed, and apower source for applying voltage between the positive electrode and thenegative electrode, wherein a target object to be processed is placed ona side of the positive electrode opposite to the side where the negativeelectrode is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows crystal structure of 12CaO.7Al₂O₃ (C12A7) as a typicalstructure of a calcium-aluminum composite oxide;

FIG. 2 is an illustration for explaining an embodiment of an apparatusfor producing negatively charged oxygen atoms according to the presentinvention;

FIG. 3 is an illustration for explaining another embodiment of theapparatus for producing negatively charged oxygen atoms according to thepresent invention;

FIG. 4 is an illustration for explaining an example of a manufacturingequipment of a semiconductor device including an apparatus for producingnegatively charged oxygen atoms according to the present invention;

FIGS. 5(A), 5(B) are illustrations for explaining another embodiment ofthe apparatus for producing negatively charged oxygen atoms according tothe present invention;

FIG. 6 is an illustration for explaining an example of a processingequipment including an apparatus for producing negatively charged oxygenatoms according to the present invention;

FIG. 7 is a graph for explaining results of mass spectroscopy; and

FIG. 8 is a graph for explaining results of X-ray photoelectronspectroscopy analysis.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention was made based on a find that the following methodis capable of producing negatively charged oxygen atoms withoutrequiring a large amount of discharge energy which is conventionallyrequired. The method comprising: placing a negative electrode on a layermade of calcium-aluminum composite oxide, placing a positive electrodein a space apart from the layer made of the calcium-aluminum compositeoxide on a side opposite to the side where the negative electrode isplaced, and applying a relatively low voltage between the negativeelectrode and the positive electrode.

That is, it was found that the calcium-aluminum composite oxideamazingly exhibits excellent effect of emitting negatively chargedoxygen atoms from the inside thereof to the outside when applied with avoltage.

Though it is not known exactly why the calcium-aluminum composite oxideemits negatively charged oxygen atoms when applied with a voltage, thereasons may be conjectured from the followings.

FIG. 1 shows a crystal structure of 12CaO.7Al₂O₃ (C12A7) as a typicalstructure of a calcium-aluminum composite oxide.

Oxygen molecule (O₂) in ambient atmosphere is trapped in the crystalstructure of C12A7 and reacts with free oxygen ion (O²⁻) existing insidethereof so that O²⁻ is converted to a pair of O²⁻ ion and O⁻ ion.

During a voltage is applied to C12A7, O⁻ ions pass through the crystallattice and are thus emitted as O⁻ ions, O²⁻ ions may be not emittedbecause O²⁻ ions have larger diameter.

The calcium-aluminum composite oxide can be made up of calcium sourceand aluminum source in oxidation atmosphere. Though the raw material maybe any of compounds each containing elements which evaporate as gaseswhen the compound is baked and are not left in a baked matter, suchcompounds including carbonates, organic acid chlorides, hydroxides, andoxides. However, the preferable raw material is a mixture of calciumcarbonate and aluminum oxide.

The case of using the mixture of calcium carbonate and aluminum oxidewill be described. The mixing ratio between calcium carbonate andaluminum oxide is preferably adjusted such that the molar ratiotherebetween is 12/7.

The baking of the mixture of calcium carbonate and aluminum oxide ispreferably performed in atmosphere in which oxygen partial pressure andwater vapor partial pressure are adjusted. The oxygen partial pressureis preferably adjusted to be 10.1 kPa or more. The atmosphere maycontain inert gas such as argon as well as oxygen.

If the oxygen partial pressure is insufficient, the amount of oxygenmolecule to be taken into crystal structure during forming reactionprocess of a calcium-aluminum composite oxide must be small, thusreducing the production efficiency of negatively charged oxygen atoms.

The water vapor partial pressure is preferably 100 Pa or less, morepreferably 10 Pa or less. That is, dry oxygen atmosphere is preferable.

When a large quantity of moisture exists in oxygen atmosphere, OH⁻ ionsin the moisture are taken in the baked matter so as to reduce theefficiency of uptake of oxygen into the crystal structure.

The atmosphere containing oxygen may be air or a mixture of oxygen andan inert gas such as nitrogen or argon gas. To prepare a highly-purifiedcomposite oxide composed of calcium carbonate and aluminum oxide, it ispreferable to use highly-purified oxygen or a mixture of oxygen and aninert gas atmosphere.

The temperature of baking the calcium carbonate and the aluminum oxideis preferably 1200° C. or more, more preferably from 1300° C. to 1450°C.

The time period of baking is preferably from 4 to 8 hours, morepreferably from 5 to 7 hours.

The calcium-aluminum composite oxide may be formed in a predeterminedconfiguration to be a self-standing member. Alternatively, acalcium-aluminum composite oxide layer may be formed on a poroussubstrate having heat resistance.

Examples of methods for forming the member of calcium-aluminum compositeoxide or the calcium-aluminum composite oxide layer include a method ofbaking a molded body made of powder or a coating layer and coatingmethods not transforming oxides of raw material such as plasma sprayingand sputtering.

In both the case of forming the self-standing member and the case offorming the calcium-aluminum composite oxide layer on the poroussubstrate having heat resistance, it is preferable to form a densemember or a dense layer not permitting the transmission of gas.

In case of forming a molded body by baking, a binder blended in thecalcium-aluminum composite oxide may affect the generation of negativelycharged oxygen atoms. Therefore, it is preferable to bake a molded bodywhich was molded without using a binder. To achieve this, thecalcium-aluminum composite oxide is preferably molded under pressure bypress molding, HIP molding, or the like and, after that, is baked.

The baking is preferably carried out at a temperature of 1200° C. ormore, preferably a temperature of from 1300° C. to 1450° C. The timeperiod of baking is preferably from 4 to 8 hours, more preferably from 5to 7 hours.

The configuration and size of the baked body from the molded body may beany configuration and any size according to the correspondingapplication. The configuration and structure are preferably decidedconsidering the transmission rate of gas of the obtained molded body andthe pressure to be applied to the baked body.

An apparatus for producing negatively charged oxygen atoms of thepresent invention will be described with reference to drawings.

FIG. 2 is an illustration for explaining an embodiment of an apparatusfor producing negatively charged oxygen atoms according to the presentinvention.

An apparatus 1 for producing negatively charged oxygen atoms comprises abaked body 2 made of a calcium-aluminum composite oxide, a negativeelectrode 3 disposed on a surface of the baked body 2, and a heatingmeans 4 such as an electric heater for heating the baked body.

The inside of the apparatus 1 is divided by a partition wall 5 into anoxygen supply compartment 6 and a negatively charged oxygen atomproducing compartment 7.

Connected to the oxygen supply compartment 6 is an oxygen supply source8. Connected to the negatively charged oxygen atom producing compartment7 is a vacuum device 9.

In the negatively charged oxygen atom producing compartment 7, apositive electrode 10 is disposed apart from the baked body 2. Theapparatus 1 is provided with a power source 11 applying voltage betweenthe negative electrode 3 and the positive electrode 10 and with anampere meter 12 for measuring current flowing between the electrodes.

In the negatively charged oxygen atom producing compartment 7, aquadrupole lens 13 for controlling the direction and focusing thenegatively charged oxygen atom beam and a target 14 are disposed.

Hereinafter, description will be made as regard to main components.

The negative electrode 3 disposed on the surface of the baked body 2 maybe made of any of materials capable of allowing current application tothe baked body. However, since the negative electrode 3 is arranged inthe oxygen supply compartment 6, the negative electrode 3 is preferablymade of a conductive material such as a metal or a conductive metaloxide which is not oxidized or not corroded even when heated in oxygenatmosphere. That is, preferable materials are noble metals such as goldand platinum, nickel, and stainless steel. Among them, gold and platinumare especially preferable.

Examples of methods for forming the negative electrode 3 on the surfaceof the baked body 2 include a method of applying a conductivecomposition containing a metal, a conductive material for forming anelectrode onto the baked body, a method of depositing a metal forforming an electrode by vacuum deposition process such as sputtering orchemical vapor deposition (CVD), and a method of attaching a mesh-likemetal to the baked body. Among these methods, the method of applying aconductive composition to the baked body has the advantage of being ableto form the electrode into any configuration.

It is believed that oxygen molecule adheres to the metal electrodeformed on the surface of the baked body so as to generate oxygen ionsand is introduced into the baked body. Therefore, the electrode to beformed on the surface of the baked body is preferably made of a noblemetal such as platinum which advantageously acts to promote adhesion andionization of oxygen molecule.

The thickness of the cathode is in a range of from 0.1 μm to 50 μm,preferably from 0.5 μm to 10 μm, in terms of strength and easiness ofhandling.

The heating means 4 for the baked body 2 may be disposed not only incontact with the baked body as shown in FIG. 2 but also at some distancefrom the baked body. In this case, the heating means may be an infraredlamp, a high-frequency induction heating device, or the like.

The examples of material of the positive electrode 10 include alloyssuch as stainless steel, noble metals such as gold and platinum, andmetals such as nickel which are stable against oxygen. Among these,stainless steel (for example, SUS304 or SUS430) which can be easilyhandled and has great durability is preferable. The positive electrode10 may have a rod-like body, a wire-like body, a mesh-like body, aplate-like body, or a disk-like body having an opening 10 a formed atthe center thereof as shown in FIG. 2.

Alternatively, a member made of a material not having conductivity onwhich a film or layer made of such a metal by sputtering or chemicalvapor deposition may be used.

The distance between the baked body 2 and the positive electrode 10 isin a range of from 5 to 100 mm, preferably from 10 to 50 mm, morepreferably from 10 to 30 mm for the purpose of effective utilizinggenerated negatively charged oxygen ions and generaging negativelycharged oxygen atoms at a low voltage.

The production of negatively charged oxygen atoms is carried out afterthe inside of the negatively charged oxygen atom producing compartment 7is vacuumed by the vacuum device 9 connected to the negatively chargedoxygen atom producing compartment 7 in order to prevent generatednegatively charge oxygen atoms from vanishing due to collision withmoisture and the like in the air.

In the state that oxygen is supplied to the oxygen supply compartment 6,the baked body 2 is heated by the heating means 4 and, at the same time,power is supplied to the negative electrode 3 and the positive electrode10 from the power source 11, thereby sequentially generating negativelycharged oxygen atoms A so that the generated negatively charged oxygenatoms A reach the target 14 disposed inside the negatively chargedoxygen atom producing compartment.

In order to observe the generation of negatively charged oxygen atoms inthe negatively charged oxygen atom producing compartment, the inside ofthe negatively charged oxygen atom producing compartment is vacuumed tohave a degree of vacuum of 0.13 Pa or less and the detection is carriedout by using a secondary electron multiplier (SEM) to the target 14.

In case of forming an oxidized film on a surface of a silicon wafer, thesilicon wafer is disposed in place of the target.

When the inside of the negatively charged oxygen atom producingcompartment is filled with a rare gas such as a helium gas or an argongas, generated negatively charged oxygen atoms can be prevented fromvanishing due to the reaction so that it is not necessary to vacuum theinside of the negatively charged oxygen atom producing compartment.

The position where the target is placed is a position so enough closerto the baked body that generated negatively charged oxygen atoms canreach and is from 1 to 100 mm, preferably from 5 to 50 mm from the bakedbody.

The potential difference between the negative electrode and the positiveelectrode is in a range of from 1 to 2000 V/cm, preferably from 10 to1000 V/cm, more preferably from 50 to 500 V/cm. In case of 1 V/cm orless, the productivity is low. In case of 2000 V/cm or more, the bakedbody or the electrodes may be damaged.

The power source for applying voltage may be any power source such as abuttery, a rectified power source, or the like.

The baked body is preferably heated at a temperature of from 200° C. to1000° C., more preferably from 500° C. to 800° C. In case of 200° C. orless, the generation efficiency is insufficient. In case of 1000° C. ormore, it is required to use special heat-resistance material andtherefore it is not preferable.

In the apparatus for producing negatively charged oxygen atoms of thepresent invention, the generation of negatively charged oxygen atoms canbe stopped by stopping the application of voltage. Therefore, the startand stop of generation of negatively charged oxygen atoms can becontrolled by ON-OFF operation of the power source. Further, accordingto the present invention, the generation amount of negatively chargedoxygen atoms can be suitably controlled by adjusting the voltage betweenthe positive electrode and the negative electrode.

While voltage is applied between the electrodes, oxygen as the rawmaterial for generating negatively charged oxygen atoms is supplied fromoxygen supply means such as air, thereby generating negatively chargedoxygen atoms.

FIG. 3 is an illustration for explaining another embodiment of theapparatus for producing negatively charged oxygen atoms according to thepresent invention.

An apparatus 1 for producing negatively charged oxygen atoms shown inFIG. 3 comprises a hollow baked body 2 a made of a calcium-aluminumcomposite oxide, a negative electrode 3 disposed inside the baked body 2a, and a heating means 4 such as an electric heater for heating thebaked body which is disposed on the outer periphery of the baked body 2a. The inside of the apparatus 1 is divided into a negatively chargedoxygen atom producing compartment 7 which is outside of the hollow bakedbody 2 a and an oxygen supply compartment 6 which is inside of thehollow baked body 2 a. Connected to the negatively charged oxygen atomproducing compartment 7 is a vacuum device 9.

In the negatively charged oxygen atom producing compartment 7, apositive electrode 10 is disposed apart from the baked body 2 a and hasan opening 10 a formed at the center thereof. The apparatus 1 isprovided with a power source 11 applying voltage between the negativeelectrode 3 and the positive electrode 10 and with an ampere meter 12for measuring current flowing between the electrodes.

In the apparatus for producing negatively charged oxygen atoms shown inFIG. 3, negatively charged oxygen atoms A are generated by the sameoperation as that of the apparatus shown in FIG. 2.

FIG. 4 is an illustration for explaining an example of a processingequipment for a semiconductor device including an apparatus forproducing negatively charged oxygen atoms according to the presentinvention.

A processing equipment 20 for a semiconductor device has a processingchamber 21 and is provided with an apparatus for producing negativelycharged oxygen atoms on an upper part of the processing chamber 21. Theapparatus comprises a baked body 2 made of a calcium-aluminum compositeoxide, a negative electrode 3 disposed on a surface of the baked body 2,and a heating means 4 such as an electric heater for heating the bakedbody. The inside of the processing equipment 20 is divided by apartition wall 5 into an oxygen supply compartment 6 and the processingchamber 21.

Connected to the oxygen supply compartment 6 is an oxygen supply source8. Connected to the processing chamber 21 is a vacuum device 9.

In the processing chamber 21, a substrate pallet 22 having electricalconductivity is arranged and a semiconductor substrate 23 is placed onthe substrate pallet 22. The substrate pallet 22 is connected to thepositive pole of a power source so that voltage is applied to thesubstrate pallet 22.

After the processing chamber 21 is vacuumed by the vacuum device 9 tohave a predetermined degree of vacuum, the baked body 2 is heated andoxygen is supplied to the oxygen supply compartment 6. In this state,voltage is applied to the negative electrode and the substrate palletwhich functions as a positive electrode, thereby generating negativelycharged oxygen atoms A so that the generated negatively charged oxygenatoms A reach the semiconductor substrate 23 and thereby permittingvarious processes to the semiconductor substrate.

By adjusting the irradiation area, the negatively charged oxygen atomscan be adopted as fine-processing means or a processing means for theentire surface of the semiconductor substrate.

As an example of processes, silicon is oxidized by reaction withnegatively charged oxygen atoms A, thereby forming an oxidized film.

According to the method for producing negatively charged oxygen atoms ofthe present invention, the generation amount of negatively chargedoxygen atoms can be greatly changed by changing the voltage to beapplied to the calcium-aluminum composite oxide, thereby making itpossible to form oxidized films of various thicknesses from an ultrathinoxidized film such as a nanometre-scale oxidized film to a thickoxidized film.

Since the negatively charged oxygen atoms of the present invention havelarge oxidizing capability, the negatively charged oxygen atoms can beused for the ashing process for decomposing and removing a resist formedon the semiconductor substrate.

Conventionally, oxygen plasma is generally used for the ashing process.Since the oxygen plasma contains large component of energy producedsimultaneously, the oxygen plasma may cause adverse effects onsemiconductor devices to be manufactured. On the other hand, theapparatus for producing negatively charged oxygen atoms of the presentinvention produces negatively charged oxygen atoms only so that it nevercause adverse effects on semiconductor devices.

In case of a resist altered by ion implantation or inorganic material,the resist is hardly removed by oxygen plasma. Even in this case, theresist can be removed for a short period of time because of largereactivity of negatively charged oxygen atoms.

FIGS. 5(A), 5(B) are illustrations for explaining another embodiment ofthe apparatus for producing negatively charged oxygen atoms according tothe present invention.

FIG. 5(A) is an illustration showing the entire structure of theapparatus for producing negatively charged oxygen atoms.

An apparatus 1 for producing negatively charged oxygen atoms comprises abaked body 2 made of a calcium-aluminum composite oxide, a negativeelectrode 3 disposed on a surface of the baked body 2, and a heatingmeans 4 such as an electric heater for heating the baked body. Theinside of the apparatus 1 is divided by a partition wall 5 into anoxygen supply compartment 6 and a negatively charged oxygen atomproducing compartment 7.

Connected to the oxygen supply compartment 6 is an oxygen supply source8. Connected to the negatively charged oxygen atom producing compartment7 is a vacuum device 9.

In the negatively charged oxygen atom producing compartment 7, a spacer24 is disposed on a surface of the baked body 2 opposite to the surfaceon which the negative electrode 3 is disposed, and a positive electrode25 is arranged above the spacer 24. Voltage is applied between thenegative electrode 3 and the positive electrode 25 from a power source11.

The negative electrode 3 and the positive electrode 25 are disposed toface each other via the baked body 2 and the spacer 24 so that thedistance therebetween is shorter than that in case that the positiveelectrode is disposed in a space. Therefore, large electric fieldintensity can be imparted to the baked body 2 even with smaller voltage.

A control electrode 26 is provided. Therefore, the flow of negativelycharged oxygen atoms A extracted from the positive electrode side can becontrolled by applying voltage from a control power source 27. As aresult of this, negatively charged oxygen atoms can be projected to adesired portion of a target object 28 to be processed so that it ispossible to form an oxide on a surface of the target object 28 or toremove material on a surface of the target object 28.

As for the spacer 24, ceramics of various types which is stable in theoxidation environment can be used. The spacer 24 may be made of alumina,silica, titania, zirconia, or the like.

The spacer 24 is obtained by forming a member having a large number ofopenings made of a ceramic such as alumina, silica, titania, orzirconia, and a forming an electrode made of a metal on a surface of themember, and is closely attached to the calcium-aluminum composite oxide.

As an alternative way, the spacer may be obtained by forming a film onthe calcium-aluminum composite oxide by a vacuum deposition process suchas plasma spraying of alumina, silica, titania, or zirconia, thenforming a metal electrode layer, and forming openings for extractingnegatively charged oxygen atoms by using a mask having a predeterminedopening pattern.

FIG. 5(B) is a top view showing an example of the spacer.

The spacer 24 can comprise a lattice-like member as shown in FIG. 5(B)or a perforated plate and a positive electrode laminated on the surfaceof the lattice-like member or the perforated plate, thereby making itpossible to apply uniform electric filed to the entire surface of thebaked body. Accordingly, negatively charged oxygen atoms can be emittedfrom the entire surface of the baked body. The positive electrode can belaminated on the surface of the spacer or formed directly on the surfaceof the spacer.

FIG. 6 is an illustration for explaining an example of a processingequipment including an apparatus for producing negatively charged oxygenatoms according to the present invention.

A processing equipment 20 has a processing chamber 21 and is providedwith an apparatus 1 for producing negatively charged oxygen atoms in alower part of the processing chamber 21. The apparatus comprises a bakedbody 2 made of a calcium-aluminum composite oxide, a negative electrode3 disposed on a surface of the baked body 2, and a heating means 4 suchas an electric heater for heating the baked body. The inside of theequipment 20 is divided by a partition wall 5 into an oxygen supplycompartment 6 and the processing chamber 21.

Connected to the oxygen supply compartment 6 is an oxygen supply source8. Connected to the processing chamber 21 is a vacuum device 9.

In the processing chamber 21, voltage is applied between a conductivetarget object 26 to be processed and the negative electrode. The targetobject functions also as a positive electrode for extracting negativelycharged oxygen atoms so that the negatively charged oxygen atomsextracted from the baked body 2 reach a surface of the target object soas to oxidize the surface or remove material from the surface.

Hereinafter, the present invention will be further detailed by means ofthe following Examples.

EXAMPLE 1

Calcium carbonate and aluminum oxide of which mean particle diameter was1 μm were mixed in such a manner to set a molar ratio (CaCO₃:Al₂O₃)therebetween to be 12:7. The mixture was baked at 1350° C. for 6 hoursin dry air atmosphere to obtain baked powder.

The obtained baked powder was molded by a molding machine at 9.81 MPainto a disk-like pellet of 15 mm in diameter and 1 mm in thickness.

The pellet was heated in dry air atmosphere at 1350° C. for 6 hours toobtain a pellet-like baked body.

Gold paste (available from Nihon Kin-eki K.K.) was applied to a flatsurface of the obtained baked body, was heated to 650° C., and was driedso as to form a negative electrode made of gold having a thickness of 5μm.

As shown in FIG. 2, the baked body was installed to the partition wall.In the negatively charged oxygen atom producing compartment, a mesh-likepositive electrode made of stainless steel (SUS304) was disposed at aposition to have a distance of 10 mm from the negative electrode.

A secondary electron multiplier was placed as a target at a position 100mm apart from the positive electrode.

The inner pressure of the negatively charged oxygen atom producingcompartment was reduced to be 1×10⁻³ Pa. However, there was no leak fromthe baked body.

In the state that the inner pressure of the negatively charged oxygenatom producing compartment was kept at 1×10⁻³ Pa, the temperature of thebaked body was increased to 700° C. by a heater mounted on the bakedbody and voltage of 500 V was applied between the positive electrode andthe negative electrode. As a result of this, an electric current of 1 μAbetween the electrodes was observed by an ampere meter 12.

Negatively charged oxygen atoms from the secondary electron multiplierwere analyzed by a quadrupole mass spectrometer with applying voltage.In this manner, the mass spectroscopy was carried out. The result isshown in FIG. 7.

A peak was observed at a mass number 16. That is, the generation ofnegatively charged oxygen atoms was confirmed.

EXAMPLE 2

Baked powder made of a calcium-aluminum composite oxide which wasprepared under the same condition as that of Example 1 was molded by amolding machine at 9.81 MPa into a cylindrical molded body of 200 mm inlength, 20 mm in outer diameter, and 18 mm in inner diameter.

The molded body was heated in dry air atmosphere at 1350° C. for 6 hoursto obtain a cylindrical baked body.

Gold paste (available from Nihon Kin-eki K.K.) was applied to the innersurface of the obtained baked body, was heated to 650° C., and was driedso as to form an electrode made of gold having a thickness of 5 μm onthe inner surface.

As shown in FIG. 3, the baked body was installed to the vessel. In thenegatively charged oxygen atom producing compartment, a mesh-likepositive electrode made of stainless steel (SUS304) was disposed at aposition to have a distance of 10 mm from the negative electrode.

A secondary electron multiplier was placed as a target at a position 100mm apart from the positive electrode.

The inner pressure of the negatively charged oxygen atom producingcompartment was reduced to be 1.33×10⁻³ Pa. However, there was no leakfrom the baked body.

Then, the temperature of the baked body was increased to 700° C. by aheater mounted on the baked body and voltage of 500 V was appliedbetween the positive electrode and the negative electrode. As a resultof this, an electric current of 3 μA between the electrodes was observedby an ampere meter 12.

After that, negatively charged oxygen atoms from the secondary electronmultiplier were analyzed by a quadrupole mass spectrometer with applyingvoltage. In this manner, the mass spectroscopy was carried out. Theresult of the mass spectroscopy after a lapse of 2 hours from theapplication of voltage was observed and was equal to the result shown inFIG. 7.

From the result, it was found that negatively charged oxygen atoms aregenerated sequentially by applying voltage.

EXAMPLE 3

Negatively charged oxygen atoms were generated in the same manner asExample 2 except that a silicon wafer of 20 mm in diameter and 1 mm inthickness was mounted as a target. The silicon wafer was irradiated withthus generated negatively charged oxygen for 30 minutes.

The thickness of an oxidized film formed on the silicon wafer afterirradiation was measured by a film thickness meter (ESM-1A ellipsometer,available from ULVAC, Inc.) and was 25 nm. As for the formed film, thecomposition of the film which was etched by argon was observed by anX-ray photoelectron spectrometer (ESCA-3200, available from ShimadzuCorporation). The result was shown in FIG. 8. It was confirmed thatsilicon oxide (SiO₂) was produced on the surface.

COMPARATIVE EXAMPLE 1

Test was conducted in the same manner as Example 2 except that an yttriastabilized Zirconia solid electrolyte cylinder (available from Nikkato)of 200 mm in length, 20 mm in outer diameter, and 2 mm in inner diameterwas used instead of the cylindrical molded body made of calcium-aluminumcomposite oxide. Measurement was carried out in the same manner asExample 2.

Measured electric current was 3 nA of which value was {fraction(1/1000)} of that of Example 2. This means that only a slight amount ofnegatively charged oxygen atoms were generated.

INDUSTRIAL APPLICABILITY

The present invention utilizes characteristics of calcium-aluminumcomposite oxide so as to enable to efficiently produce negativelycharged oxygen atoms without requiring great discharge energy and isvery useful in various fields, for example, for various oxidativereactions, fabrication of silicon oxidized film in semiconductormanufacturing process, ashing process, mildew-proof treatment of foodproducts, and maintaining sea food freshness.

1. A method for producing negatively charged oxygen atoms comprising:placing a negative electrode on a surface of a member made ofcalcium-aluminum composite oxide of which a molar ratio between calciumoxide and aluminum oxide is 12:7; proximately placing a positiveelectrode on a side of the member opposite to the surface on which thenegative electrode is placed; supplying oxygen to the negative electrodeside; and applying voltage between the negative electrode and thepositive electrode so as to extract negatively charged oxygen atoms fromthe side where the positive electrode is placed.
 2. A method forproducing negatively charged oxygen atoms as claimed in claim 1, whereinthe voltage is applied while heating the member to a temperature of from200° C. to 1000° C.
 3. A method for producing negatively charged oxygenatoms as claimed in claim 1, wherein the calcium-aluminum compositeoxide is prepared by baking a mixture of calcium carbonate and aluminumoxide.
 4. A method for producing negatively charged oxygen atoms asclaimed in claim 3, wherein the calcium-aluminum composite oxide isprepared by baking the calcium carbonate and the aluminum oxide at abaking temperature of from 1300° C. to 1450° C.
 5. A method forproducing negatively charged oxygen atoms as claimed in claim 3, whereinthe calcium carbonate and the aluminum oxide are baked in dry oxygenatmosphere of which oxygen partial pressure is 10 kPa or more and thewater vapor partial pressure is 10⁻³ Pa or less.
 6. (Canceled)
 7. Anapparatus for producing negatively charged oxygen atoms having an oxygensupply compartment and a negatively charged oxygen atom producingcompartment which are defined by arranging a member made ofcalcium-aluminum composite oxide of which a molar ratio between calciumoxide and aluminum oxide is 12:7, the apparatus comprising a heatingmeans disposed on the member made of calcium-aluminum composite oxide, anegative electrode placed on a surface of the member facing the oxygensupply compartment, a positive electrode placed in the negativelycharged oxygen atom producing compartment on a side of the memberopposite to the surface on which the negative electrode is placed, and apower source for applying voltage between the positive electrode and thenegative electrode.
 8. An apparatus for producing negatively chargedoxygen atoms as claimed in claim 7, wherein the positive electrode isplaced on the side of the member made of calcium-aluminum compositeoxide opposite to the surface of the member on which the negativeelectrode is placed such that the positive electrode is spaced apartfrom the member made of calcium-aluminum composite oxide.
 9. Anapparatus for producing negatively charged oxygen atoms as claimed inclaim 8, wherein in place of the positive electrode, a conductive targetobject to be processed is placed on the side of the member made ofcalcium-aluminum composite oxide opposite to the surface of the memberon which the negative electrode is placed such that the conductivetarget object is spaced apart from tile member made of calcium-aluminumcomposite oxide, and wherein voltage is applied between the conductivetarget object and the negative electrode.
 10. An apparatus for producingnegatively charged oxygen atoms as claimed in claim 7, wherein thepositive electrode is placed on a spacer which is attached to thesurface of the member made of calcium-aluminum composite oxide oppositeto the surface of the member on which the negative electrode is placed.11. An apparatus for producing negatively charged oxygen atoms asclaimed in claim 9, wherein a control electrode is arranged between thepositive electrode and the target object to be processed with negativelycharged oxygen atoms.
 12. An apparatus for producing negatively chargedoxygen atoms as claimed in claim 7, wherein the calcium-aluminumcomposite oxide is prepared by baking a mixture of calcium carbonate andaluminum oxide.
 13. (Canceled)
 14. A processing equipment for conductingprocess by negatively charged oxygen atoms having an oxygen supplycompartment and a negatively charged oxygen atom producing compartmentwhich are defined by arranging a member made of calcium-aluminumcomposite oxide of which a molar ratio between calcium oxide andaluminum oxide is 12:7, the processing equipment comprising a heatingmeans disposed on the member made of calcium-aluminum composite oxide, anegative electrode placed on a surface of the member facing the oxygensupply compartment, a positive electrode placed in the negativelycharged oxygen atom producing compartment on a side of the memberopposite to the surface on which the negative electrode is placed, and apower source for applying voltage between the positive electrode and thenegative electrode, wherein a target object to be processed is placed ona side of the positive electrode opposite to the side where the negativeelectrode is provided.